System and Method for Pilot Design

ABSTRACT

An apparatus for generating a pilot pattern for data to be transmitted in an orthogonal frequency-division multiplexing (OFDM) based communication system, having a for allocating pilot symbols for a plurality of data streams to form a plurality of pilot clusters in the pilot pattern, wherein each of the pilot clusters includes ones of the pilot symbols, the ones of the pilot symbols being for respectively different ones of the data streams. The apparatus also includes a mechanism for moving at least one of the pilot clusters from a first location in the resource block to a second location in the resource block to generate a second pilot pattern, the first and second locations being symmetrical in time, and a mechanism for generating a third pilot pattern based on the first and second pilot patterns.

RELATED APPLICATIONS

This application is a Continuation of pending U.S. patent applicationSer. No. 12/431,046, filed on Apr. 28, 2009 and entitled “SYSTEM ANDMETHOD FOR PILOT DESIGN”, which claims the benefit of priority from U.S.Provisional Patent Application No. 61/050,977, filed May 6, 2008, U.S.Provisional Patent Application No. 61/079,986, filed Jul. 11, 2008, andU.S. Provisional Patent Application No. 61/093,520, filed Sep. 2, 2008,the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to systems and methods for pilot design for datato be transmitted in a wireless communication network.

BACKGROUND

Wireless communication techniques based on multiple subcarriers, such asan orthogonal frequency-division multiplexing (OFDM) technique, aregaining worldwide popularity due to their broad applications. Forexample, an OFDM based communication system may be used in a pluralityof networks including Worldwide Interoperability for Microwave Access(WiMax) networks, Wireless Fidelity (Wi-Fi) networks, Wireless Broadband(WiBro) networks, etc.

The OFDM technique uses a plurality of closely-spaced orthogonalsubcarriers to carry data. For example, the data may be allocated on aplurality of parallel data channels, one for each of the subcarriers.Each of the subcarriers may be modulated with a conventional modulationscheme, e.g., quadrature amplitude modulation, at a relatively lowsymbol rate. In addition, based on the OFDM technique, an inverse fastFourier transform (IFFT) may be performed on OFDM symbols representingthe data on a transmitter side of the OFDM based communication system,and a fast Fourier transform (FFT) may be performed to recover the OFDMsymbols on a receiver side of the OFDM based communication system.Signals including the OFDM symbols are transmitted from the transmitterside to the receiver side through a communication channel.

In reality, the communication channel may have an effect on the signalswhen the signals are transmitted. The receiver side may need knowledgeof the communication channel to remove such effect, in order toaccurately recover the data. To facilitate estimation of thecommunication channel, signals known to both the transmitter side andthe receiver side, i.e., pilot symbols, may be inserted in OFDM symbolson the transmitter side. The receiver side may perform channelestimation based on resource blocks in received signals, and each of theresource blocks includes a plurality of OFDM symbols and, hence, pilotsymbols.

For example, the transmitter side may transmit signals including OFDMsymbols from multiple transmitting antennas simultaneously, and each ofthe transmitting antennas transmits one data stream. Multiple receivingantennas on the receiver side each may receive the signals transmittedfrom the multiple transmitting antennas.

SUMMARY

According to a first aspect of the present disclosure, there is provideda method for generating a pilot pattern for data to be transmitted in anorthogonal frequency-division multiplexing (OFDM) based communicationsystem, the method comprising: allocating pilot symbols for a pluralityof data streams to form a plurality of pilot clusters in the pilotpattern, wherein each of the pilot clusters includes ones of the pilotsymbols, the ones of the pilot symbols being for respectively differentones of the data streams.

According to a second aspect of the present disclosure, there isprovided an apparatus for generating a pilot pattern for data to betransmitted in an orthogonal frequency-division multiplexing (OFDM)based communication system, the apparatus being configured to: allocatepilot symbols for a plurality of data streams to form a plurality ofpilot clusters in the pilot pattern, wherein each of the pilot clustersincludes ones of the pilot symbols, the ones of the pilot symbols beingfor respectively different ones of the data streams.

According to a third aspect of the present disclosure, there is provideda method for generating a pilot pattern for data to be transmitted in anorthogonal frequency-division multiplexing (OFDM) based communicationsystem, the method comprising: allocating first and second pilot symbolsfor first and second ones of a plurality of data streams, respectively,to a same subcarrier of the communication system, the first and secondpilot symbols corresponding to a same time.

According to a fourth aspect of the present disclosure, there isprovided an apparatus for generating a pilot pattern for data to betransmitted in an orthogonal frequency-division multiplexing (OFDM)based communication system, the apparatus being configured to: allocatefirst and second pilot symbols for first and second ones of a pluralityof data streams, respectively, to a same subcarrier of the communicationsystem, the first and second pilot symbols corresponding to a same time.

According to a fifth aspect of the present disclosure, there is providedan orthogonal frequency-division multiplexing (OFDM) based communicationsystem for transmitting a plurality of data streams, the system beingconfigured to: allocate pilot symbols for the plurality of data streamsto form a plurality of pilot clusters in a pilot pattern, wherein eachof the pilot clusters includes ones of the pilot symbols, the ones ofthe pilot symbols being for respectively different ones of the datastreams.

According to a sixth aspect of the present disclosure, there is providedan orthogonal frequency-division multiplexing (OFDM) based communicationsystem transmitting a plurality of data streams, the system beingconfigured to: allocate first and second pilot symbols for first andsecond ones of a plurality of data streams, respectively, to a samesubcarrier of the communication system, the first and second pilotsymbols corresponding to a same time.

According to a seventh aspect of the present disclosure, there isprovided a method for generating a pilot pattern for data to betransmitted in an orthogonal frequency-division multiplexing (OFDM)based communication system, the method comprising: allocating aplurality of pilot symbols for a data stream such that ones of theplurality of pilot symbols are uniformly distributed in the pilotpattern.

According to an eighth aspect of the present disclosure, there isprovided a method for generating a new pilot pattern for data to betransmitted in an orthogonal frequency-division multiplexing (OFDM)based communication system, the method comprising: generating the newpilot pattern based on a given pilot pattern including a plurality ofpilot symbols.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 illustrates a method for pilot design for data to be transmittedin a wireless communication system, according to an exemplaryembodiment.

FIG. 2 shows a pilot design example, according to an exemplaryembodiment.

FIG. 3 illustrates a method for pilot design for data to be transmittedin a wireless communication system, according to an exemplaryembodiment.

FIG. 4 shows a pilot design example, according to an exemplaryembodiment.

FIG. 5 illustrates a method for pilot design for data to be transmittedin a wireless communication system, according to an exemplaryembodiment.

FIG. 6 illustrates a method for pilot design for data to be transmittedin a wireless communication system, according to an exemplaryembodiment.

FIG. 7 shows a pilot design example, according to an exemplaryembodiment.

FIG. 8 illustrates a method for pilot design for data to be transmittedin a wireless communication system, according to an exemplaryembodiment.

FIG. 9 shows a pilot design example, according to an exemplaryembodiment.

FIG. 10 shows a pilot design example, according to an exemplaryembodiment.

FIG. 11 shows a pilot design example, according to an exemplaryembodiment.

FIG. 12 shows a pilot design example, according to an exemplaryembodiment.

FIG. 13 shows a pilot design example, according to an exemplaryembodiment.

FIG. 14 shows a pilot design example, according to an exemplaryembodiment.

FIG. 15 shows a pilot design example, according to an exemplaryembodiment.

FIGS. 16-24 show exemplary pilot patterns, according to exemplaryembodiments.

FIGS. 25-30 show exemplary pilot patterns, according to exemplaryembodiments.

FIG. 31 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIGS. 32A and 32B show exemplary, new pilot patterns generated based ona given pilot pattern, according to an exemplary embodiment.

FIG. 33 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIG. 34 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIG. 35 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIG. 36 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIG. 37 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIG. 38 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment.

FIGS. 39-42 show exemplary pilot patterns for long delay spreadchannels, according to exemplary embodiments.

FIG. 43 illustrates an apparatus for generating a pilot pattern for datato be transmitted in the above noted OFDM based communication system,according to an exemplary embodiment

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments consistent with thepresent invention do not represent all implementations consistent withthe invention. Instead, they are merely examples of systems and methodsconsistent with aspects related to the invention as recited in theappended claims.

In exemplary embodiments, there are provided methods for pilot designfor data to be transmitted in a wireless communication system. Forillustrative purposes only, it is assumed the communication system is anorthogonal frequency-division multiplexing (OFDM) based communicationsystem transmitting first, second, third, and fourth data streams forembodiments illustrated in FIGS. 1-15.

FIG. 1 illustrates a method for pilot design for data to be transmittedin the above noted OFDM based communication system, according to anexemplary embodiment. Referring to FIG. 1, a resource block 100 in atime-frequency domain is used to show an exemplary pilot pattern. Forexample, a resource block may be a representation including a pluralityof contiguous OFDM symbols shown in a time frequency domain. Each row ofthe resource block 100 corresponds to a subcarrier of the communicationsystem, and each column of the resource block 100 corresponds to an OFDMsymbol. The resource block 100 includes a plurality of OFDM symbols suchas OFDM symbols S1, . . . , S6, which further include a plurality ofdata symbols each represented by a small block with a letter “D” and aplurality of pilot symbols each represented by a small block with anindexed letter P. For example, the small blocks with indexed letters“P1,” “P2,” “P3,” and “P4” represent pilot symbols for the first,second, third, and fourth data streams, respectively. In the resourceblock 100, each of the OFDM symbols S1, . . . , S6 is composed of one ofthe columns of data symbols “D” and any pilot symbols included therein.

In exemplary embodiments, the pilot pattern is generated based on amoderate-overhead scheme. As noted above, pilot symbols are known toboth a transmitter side and a receiver side of the communication system,and are inserted in OFDM symbols on the transmitter side for channelestimation on the receiver side. On one hand, pilot symbols typically donot carry information that the transmitter side intends to transmit tothe receiver side and, hence, may cause communication overhead. On theother hand, an increased number of pilot symbols inserted in OFDMsymbols may be beneficial to improve accuracy of channel estimation.

In exemplary embodiments, a plurality of pilot clusters 102-1, . . .102-6, each indicated by one of the dashed circles in FIG. 1, may beformed in the pilot pattern. A pilot cluster may include first andsecond pilot symbols allocated to adjacent subcarriers of thecommunication system in one OFDM symbol, and/or first and second pilotsymbols allocated to a same subcarrier of the communication system inadjacent OFDM symbols. In the illustrated embodiment, each of the pilotclusters 102-1, . . . 102-6 includes pilot symbols, each for one of thefirst, second, third, and fourth data streams.

In exemplary embodiments, ones of the pilot symbols may be allocated tofirst and second boundary subcarriers in the resource block 100,corresponding to the first and last rows of the resource block 100,respectively. For example, as shown FIG. 1, the pilot symbols P1 and P3in the pilot cluster 102-1 are allocated to the first boundarysubcarrier in the resource block 100. Also for example, the pilotsymbols P2 and P4 in the pilot cluster 102-3 are allocated to the secondboundary subcarrier in the resource block 100. When the ones of thepilot symbols are allocated to the first or second boundary subcarrierin the resource block 100, accuracy of channel estimation may beimproved.

In exemplary embodiments, ones of the pilot clusters 102-1, . . . 102-6may be allocated to corners of the resource block 100. For example, asshown FIG. 1, the pilot clusters 102-1, 102-3, 102-4, and 102-6 areallocated to the corners of the resource block 100. When the ones of thepilot clusters are allocated to the corners of the resource block 100,accuracy of channel estimation may be improved.

In exemplary embodiments, a pilot pattern may be generated byinterchanging positions of pilot symbols in ones of the pilot clusters102-1, . . . , 102-6 in the resource block 100. For example, thepositions of the pilot symbols P1 and P2 in each of the pilot clusters102-4, 102-5, and 102-6 may be interchanged. Also for example, thepositions of the pilot symbols P3 and P4 in each of the pilot clusters102-4, 102-5, and 102-6 may be interchanged. FIG. 2 shows a pilot designexample including the generated pilot pattern in a resource block 200,according to an exemplary embodiment.

FIG. 3 illustrates a method for pilot design for data to be transmittedin the above noted OFDM based communication system, according to anexemplary embodiment. Referring to FIG. 3, a resource block 300 in atime-frequency domain is used to show a pilot pattern, according to anexemplary embodiment. Each row of the resource block 300 corresponds toa subcarrier of the communication system, and each column of theresource block 300 corresponds to an OFDM symbol. The resource block 300includes a plurality of OFDM symbols such as OFDM symbols S1, . . . ,S6, which further include a plurality of data symbols each representedby a small block with a letter “D” and a plurality of pilot symbols eachrepresented by a small block with an indexed letter P. For example, thesmall blocks with indexed letters “P1,” “P2,” “P3,” and “P4” representpilot symbols for the first, second, third, and fourth data streams,respectively. In the resource block 300, each of the OFDM symbols S1, .. . , S6 is composed of one of the columns of data symbols “D” and anypilot symbols included therein.

In exemplary embodiments, the pilot pattern is generated based on alow-overhead scheme. In other words, the pilot pattern shown in FIG. 3includes a relatively low number of pilot symbols, which may reducecommunication overhead, compared to the pilot patterns based on themoderate-overhead scheme shown in FIGS. 1 and 2.

In exemplary embodiments, a plurality of pilot clusters 302-1, . . .302-4, each indicated by one of the dashed circles in FIG. 3, may beformed in the pilot pattern. In the illustrated embodiment, each of thepilot clusters 302-1, . . . 302-4 includes pilot symbols, each for oneof the first, second, third, and fourth data streams.

In exemplary embodiments, a pilot pattern may be generated byinterchanging positions of pilot symbols in ones of the pilot clusters302-1, . . . , 302-4 in the resource block 300. For example, thepositions of the pilot symbols P1 and P2 in each of the pilot clusters302-3 and 302-4 may be interchanged. Also for example, the positions ofthe pilot symbols P3 and P4 in each of the pilot clusters 302-3 and302-4 may be interchanged. FIG. 4 shows a pilot design example includingthe generated pilot pattern in a resource block 400, according to anexemplary embodiment.

FIG. 5 illustrates a method for pilot design for data to be transmittedin the above noted OFDM based communication system, according to anexemplary embodiment. Referring to FIG. 5, a combination of first andsecond resource blocks 500-1 and 500-2 in a time-frequency domain isused to show an exemplary pilot pattern. Each row of the resource block500-1 or 500-2 corresponds to a subcarrier of the communication system,and each column of the resource block 500-1 or 500-2 corresponds to anOFDM symbol. In addition, an i^(th) row of the resource block 500-1 andan i^(th) row of the resource block 500-2 correspond to a samesubcarrier of the communication system, and a lh column of the resourceblock 500-1 and a r column of the resource block 500-2 correspond to asame time.

The resource block 500-1 includes a plurality of OFDM symbols such asOFDM symbols S1, . . . , S6, which further include a plurality of datasymbols each represented by a small block with a letter “D” and aplurality of pilot symbols each represented by a small block with anindexed letter P. For example, the small blocks with indexed letters“P1” and “P2” represent pilot symbols for the first and second datastreams, respectively. In the resource block 500-1, each of the OFDMsymbols S1, . . . , S6 is composed of one of the columns of data symbols“D” and any pilot symbols included therein.

The resource block 500-2 includes a plurality of OFDM symbols such asOFDM symbols S1′, . . . , S6′, which correspond to the OFDM symbols S1,. . . , S6, respectively, and include a plurality of data symbols eachrepresented by a small block with a letter “D” and a plurality of pilotsymbols each represented by a small block with an indexed letter P. Forexample, the small blocks with indexed letters “P3” and “P4” representpilot symbols for the third and fourth data streams, respectively. Inthe resource block 500-2, each of the OFDM symbols S1′, . . . , S6′ iscomposed of one of the columns of data symbols “D” and any pilot symbolsincluded therein.

In exemplary embodiments, a plurality of pilot clusters 502-1, . . .502-6, each indicated by one of the dashed circles in the resource block500-1, may be formed in the pilot pattern. Each of the pilot clusters502-1, . . . 502-6 includes pilot symbols, each for one of the first andsecond data streams. Similarly, a plurality of pilot clusters 504-1, . .. 504-6, each indicated by one of the dashed circles in the resourceblock 500-2, may be formed in the pilot pattern. Each of the pilotclusters 504-1, . . . 504-6 includes pilot symbols, each for one of thethird and fourth data streams.

In exemplary embodiments, pilot symbols for different data streams maybe allocated to a same subcarrier of the communication system, theallocated pilot symbols corresponding to a same time. For example, thepilot symbol P1 in the pilot cluster 502-1 and the pilot symbol P3 inthe pilot cluster 504-1 are allocated to a same subcarrier of thecommunication system and correspond to a same time. Also for example,the pilot symbol P2 in the pilot cluster 502-3 and the pilot symbol P4in the pilot cluster 504-3 are allocated to a same subcarrier of thecommunication system and correspond to a same time.

In exemplary embodiments, pilot symbols for different data streams thatare allocated to a same subcarrier of the communication system may bemultiplied by mutually orthogonal codes, e.g., Walsh codes. As a result,generated pilot patterns may support and simplify multi-user channelestimation, and may not increase communication overhead.

For example, the pilot symbols P1 in the pilot clusters 502-1 and 502-4may be multiplied by a first code, and the pilot symbols P3 in the pilotclusters 504-1 and 504-4 may be multiplied by a second code, the firstand second codes being mutually orthogonal. Also for example, the pilotsymbols P2 in the pilot clusters 502-1 and 502-4 may be multiplied by athird code, and the pilot symbols P4 in the pilot clusters 504-1 and504-4 may be multiplied by a fourth code, the third and fourth codesbeing mutually orthogonal.

In exemplary embodiments, the pilot pattern shown in FIG. 5 is generatedbased on a moderate-overhead scheme. As noted above, pilot symbols areknown to both a transmitter side and a receiver side of a communicationsystem, and are inserted in OFDM symbols on a transmitter side forchannel estimation on a receiver side. On one hand, pilot symbolstypically do not carry information that the transmitter side intends totransmit to the receiver side and, hence, may cause communicationoverhead. On the other hand, an increased number of pilot symbolsinserted in OFDM symbols may be beneficial to improve accuracy ofchannel estimation.

In exemplary embodiments, ones of the pilot symbols may be allocated tofirst and second boundary subcarriers in each of the resource blocks500-1 and 500-2, corresponding to the first and last rows of theresource block 500-1 or 500-2, respectively. For example, the pilotsymbols P1 in the pilot clusters 502-1 and 502-4 are allocated to thefirst boundary subcarrier of the resource block 500-1, and the pilotsymbols P2 in the pilot clusters 502-3 and 502-6 are allocated to thesecond boundary subcarrier of the resource block 500-1. Also forexample, the pilot symbols P3 in the pilot clusters 504-1 and 504-4 areallocated to the first boundary subcarrier of the resource block 500-2,and the pilot symbols P4 in the pilot clusters 504-3 and 504-6 areallocated to the second boundary subcarrier of the resource block 500-2.When pilot symbols are allocated to the boundary subcarriers in theresource block 500-1 or 500-2, accuracy of channel estimation may beimproved.

FIG. 6 illustrates a method for pilot design for data to be transmittedin the above noted OFDM based communication system, according to anexemplary embodiment. Referring to FIG. 6, a combination of first andsecond resource blocks 600-1 and 600-2 in a time-frequency domain isused to show an exemplary pilot pattern. Each row of the resource block600-1 or 600-2 corresponds to a subcarrier of the communication system,and each column of the resource block 600-1 or 600-2 corresponds to anOFDM symbol. In addition, an i^(th) row of the resource block 600-1 andan i^(th) row of the resource block 600-2 correspond to a samesubcarrier of the communication system, and a j^(th) column of theresource block 600-1 and a j^(th) column of the resource block 600-2correspond to a same time.

The resource block 600-1 includes a plurality of OFDM symbols such asOFDM symbols S1, . . . , S6, which further include a plurality of datasymbols each represented by a small block with a letter “D” and aplurality of pilot symbols each represented by a small block with anindexed letter P. For example, the small blocks with indexed letters“P1” and “P2” represent pilot symbols for the first and second datastreams, respectively. In the resource block 600-1, each of the OFDMsymbols S1, . . . , S6 is composed of one of the columns of data symbols“D” and any pilot symbols included therein.

The resource block 600-2 includes a plurality of OFDM symbols such asOFDM symbols S1′, . . . , S6′, which correspond to the OFDM symbols S1,. . . , S6, respectively, and include a plurality of data symbols eachrepresented by a small block with a letter “D” and a plurality of pilotsymbols each represented by a small block with an indexed letter P. Forexample, the small blocks with indexed letters “P3” and “P4” representpilot symbols for the third and fourth data streams, respectively. Inthe resource block 600-2, each of the OFDM symbols S1′, . . . , S6′ iscomposed of one of the columns of data symbols “D” and any pilot symbolsincluded therein.

In exemplary embodiments, a plurality of pilot clusters 602-1, . . .602-4, each indicated by one of the dashed circles in the resource block600-1, may be formed in the pilot pattern. Each of the pilot clusters602-1, . . . 602-4 includes pilot symbols, each for one of the first andsecond data streams. Similarly, a plurality of pilot clusters 604-1, . .. 604-4, each indicated by one of the dashed circles in the resourceblock 600-2, may be formed in the pilot pattern. Each of the pilotclusters 604-1, . . . 604-4 includes pilot symbols, each for one of thethird and fourth data streams.

In exemplary embodiments, pilot symbols for different data streams maybe allocated to a same subcarrier of the communication system, theallocated pilot symbols corresponding to a same time. For example, thepilot symbol P1 in the pilot cluster 602-1 and the pilot symbol P3 inthe pilot cluster 604-1 are allocated to a same subcarrier of thecommunication system and correspond to a same time. Also for example,the pilot symbol P2 in the pilot cluster 602-2 and the pilot symbol P4in the pilot cluster 604-2 are allocated to a same subcarrier of thecommunication system and correspond to a same time.

In exemplary embodiments, pilot symbols for different data streams thatare allocated to a same subcarrier of the communication system may bemultiplied by mutually orthogonal codes, e.g., Walsh codes, such thatthe pilot symbols for the different data streams may be extracted on areceiver side of the communication system. As a result, generated pilotpatterns may support and simplify multi-user channel estimation, and maynot increase communication overhead.

For example, the pilot symbols P1 in the pilot clusters 602-1 and 602-3may be multiplied by a first code, and the pilot symbols P3 in the pilotclusters 604-1 and 604-3 may be multiplied by a second code, the firstand second codes being mutually orthogonal. Also for example, the pilotsymbols P2 in the pilot clusters 602-1 and 602-3 may be multiplied by athird code, and the pilot symbols P4 in the pilot clusters 604-1 and604-3 may be multiplied by a fourth code, the third and fourth codesbeing mutually orthogonal.

In exemplary embodiments, the pilot pattern is generated based on alow-overhead scheme. In other words, the pilot pattern shown in FIG. 6includes a relatively low number of pilot symbols, which may reducecommunication overhead, compared to the pilot pattern based on themoderate-overhead scheme shown in FIG. 5.

In exemplary embodiments, pilot symbols at boundary times in a resourceblock, corresponding to the first and last columns of the resourceblock, may be symmetrically shifted to intermediate times in theresource block. FIG. 7 shows a pilot design example in first and secondresource blocks 700-1 and 700-2 formed by varying the resource blocks500-1 and 500-2 (FIG. 5), respectively, by symmetrically shifting thepilot symbols in the pilot clusters 502-2 and 502-5 at boundary times ofthe resource block 500-1 to intermediate times, and symmetricallyshifting the pilot symbols in the pilot clusters 504-2 and 504-5 atboundary times of the resource block 500-2 to intermediate times,according to an exemplary embodiment.

FIG. 8 illustrates a method for pilot design for data to be transmittedin the above noted OFDM based communication system, according to anexemplary embodiment. Referring to FIG. 8, a resource block 800 in atime-frequency domain is used to show an exemplary pilot pattern. Eachrow of the resource block 800 corresponds to a subcarrier of thecommunication system, and each column of the resource block 800corresponds to an OFDM symbol. The resource block 800 includes aplurality of OFDM symbols such as OFDM symbols S1, . . . , S6, whichfurther include a plurality of data symbols each represented by a smallblock with a letter “D” and a plurality of pilot symbols eachrepresented by a small block with an indexed letter P. For example, thesmall blocks with indexed letters “P1,” “P2,” “P3,” and “P4” representpilot symbols for first, second, third, and fourth data streams,respectively. In the resource block 800, each of the OFDM symbols S1, .. . , S6 is composed of one of the columns of data symbols “D” and anypilot symbols included therein.

In exemplary embodiments, a plurality of pilot clusters 802-1, . . .802-4, each indicated by one of the dashed circles in FIG. 8, may beformed in the pilot pattern. Each of the pilot clusters 802-1, . . .802-4 includes pilot symbols, each for one of the first, second, third,and fourth data streams.

In exemplary embodiments, a pilot pattern may be generated by moving apilot cluster from a first location in a resource block to a secondlocation in the resource block, the first and second locations beingsymmetrical in time. FIG. 9 shows a pilot design example in a resourceblock 900 generated by moving each of the pilot clusters 802-1, . . .802-4 from a first location to a second location in the resource block800 (FIG. 8), the first and second locations being symmetrical in time,according to an exemplary embodiment.

In exemplary embodiments, a pilot pattern may be generated based onfirst and second pilot patterns. FIG. 10 shows a pilot design example ina resource blocks 1000 generated based on the resource block 800 (FIG.8) and the resource block 900 (FIG. 9), according to an exemplaryembodiment. For example, locations of the pilot symbols for the firstand third data streams in the resource block 1000 correspond tolocations of the pilot symbols for the first and third data streams inthe resource block 900 (FIG. 9). Also for example, locations of thepilot symbols for the second and fourth data streams in the resourceblock 1000 correspond to locations of the pilot symbols for the secondand fourth data streams in the resource block 800 (FIG. 8). Each of thepilot patterns shown in FIGS. 8-10 may provide good channel estimationwhen the communication system moves at a relatively high speed.

In exemplary embodiments, pilot symbols for a data stream may bedistributed in different OFDM symbols in a resource block. As a result,power fluctuation between the OFDM symbols may be reduced, and accuracyof channel estimation may be improved. FIG. 11 shows a pilot designexample in a resource blocks 1100 in which the pilot symbols for each ofthe first, second, third, and fourth data streams are distributed indifferent OFDM symbols, according to an exemplary embodiment. Forexample, the resource block 1100 may be generated based on the resourceblock 1000 (FIG. 10), by interchanging ones of the pilot symbols for thefirst data stream and ones of the pilot symbols for the third datastream, and interchanging ones of the pilot symbols for the second datastream and ones of the pilot symbols for the fourth data stream in theresource block 1000 (FIG. 10).

In exemplary embodiments, locations of pilot symbols in a resource blockmay be determined based on various multiple-input and multiple-output(MIMO) applications such as a space-time block codes (STBC) application,a space-frequency block codes (SFBC) application, a spatial multiplexing(SM) application, or a multi-user MIMO (MU-MIMO) application. Forexample, the pilot patterns in FIGS. 8-11 may be used in the STBC, SM,or MU-MIMO applications. Pilot patterns may also be generated for use inthe SFBC application by modifying the pilot patterns in FIGS. 8-11.

In one exemplary embodiment, positions of the pilot symbols in the pilotclusters 802-2 and 802-3 in the resource block 800 (FIG. 8) may bechanged, to generate a pilot pattern for use in the SFBC application.FIG. 12 shows a pilot design example including the generated pilotpattern in a resource block 1200, according to an exemplary embodiment.For example, each column of the resource block 1200 corresponds to anOFDM symbol, and includes an even number of consecutive data symbols.Therefore, the pilot pattern shown in the resource block 1200 may beused in the SFBC application.

FIGS. 13-15 show exemplary pilot patterns in resource blocks 1300, 1400,and 1500, respectively, for use in the SFBC application, according toexemplary embodiments. Similar to the above description in connectionwith generating the pilot pattern shown in FIG. 12, the resource blocks1300 (FIG. 13), 1400 (FIG. 14), and 1500 (FIG. 15) may be generatedbased on the resource blocks 900 (FIG. 9), 1000 (FIG. 10), and 1100(FIG. 11), respectively. As a result, each column of the resource block1300, 1400, or 1500, corresponding to an OFDM symbol, includes an evennumber of consecutive data symbols. Accordingly, the pilot patternsshown in FIGS. 13-15 may be used in the SFBC application.

In exemplary embodiments, the pilot pattern shown in each of FIGS. 1-15may be used for a single-user MIMO system or a multi-user MIMO system.For example, if the communication system is a single-user MIMO system,the first, second, third, and fourth data streams may be received byfirst, second, third, and fourth antennas of a receiver in thecommunication system, respectively. Also for example, if thecommunication system is a multiple-user MIMO system, the transmittedfirst, second, third, and fourth data streams may be received by firstand second antennas of each of first and second receivers in thecommunication system, respectively.

In exemplary embodiments, a single-stream pilot pattern for a singledata stream may be generated based on the pilot pattern for the first,second, third, and fourth data streams shown in each of FIGS. 1-15. Forexample, all the pilot symbols P1 for the first data stream may be usedas pilot symbols for the single data stream. In addition, all the pilotsymbols P2, P3, and P4 for the second, third, and fourth data streamsmay be replaced by data symbols for the single date stream.

In exemplary embodiments, different factors may be considered togenerate a pilot pattern. For example, communication overhead due topilot symbols may need to be minimized without significantly degradingaccuracy of channel estimation. Also for example, frequency spacing ofpilot symbols for a data stream may be set relatively small to providegood interpolation for a frequency-selective channel. Furthermore,extrapolation generally needs to be avoided or minimized, and boundarysubcarriers in a resource block are preferred to include pilot symbolsfor mitigating extrapolation error.

In exemplary embodiments, additional factors may be considered togenerate a pilot pattern represented by a resource block that isrelatively small. For example, a resource block including sixsubcarriers may be considered as a relatively small resource block. Whenthe resource block is relatively small, communication overhead due topilot allocation may be increased and pilot efficiency may be lowered,because a number of pilot symbols in the resource block may account fora relatively high percentage of a total number of pilot and data symbolsin that resource block. Therefore, overhead optimization may need to beconsidered to generate the pilot pattern represented by the relativelysmall resource block.

In addition, pilot symbols, compared to data symbols, typically modulatesubcarriers that have a relatively high power, which may provide anadvantage of increased reliability for channel estimation. However, thatadvantage may diminish because pilot signals from a first sector/cellmay cause interference with pilot signals from a second sector/cell thatis adjacent to the first sector/cell. Accordingly, additional factorsmay be considered to generate a pilot pattern represented by arelatively small resource block.

In exemplary embodiments, exemplary rules for designing a pilot patternrepresented by a resource block that is relatively small may includedesigning the pilot pattern to facilitate channel estimation. Forexample, a number of pilot symbols may be reduced in the resource block,such that communication overhead may be reduced. Also for example, pilotsymbols may be allocated to boundary subcarriers in the resource block,corresponding to the first and last rows of the resource block, suchthat extrapolation may be minimized or avoided when performing channelestimation based on the resource block. Further for example, pilotsymbols may be allocated to achieve a distribution in the resource blockthat is as uniform as possible. In one aspect, pilot symbols that have arelatively uniform distribution in subcarrier frequency may improveaccuracy of channel estimation. In another aspect, pilot symbols thathave a relatively uniform distribution in time may reduce powerfluctuation between OFDM symbols.

In exemplary embodiments, exemplary rules for designing a pilot patternrepresented by a resource block that is relatively small may includedesigning the pilot pattern to facilitate pilot allocation for multipledata streams, and to facilitate reduction of interference betweendifferent pilot patterns. In addition, for use in the SFBC or STBCapplication noted above, data symbols may be allocated in the resourceblock to form as many pairs of data symbols as possible. Each of thepairs of data symbols may be allocated to adjacent times correspondingto a same subcarrier frequency for the STBC application, or be allocatedto adjacent subcarrier frequencies corresponding to a same time for theSFBC application.

FIGS. 16-24 show exemplary pilot patterns designed based on theabove-described rules, according to exemplary embodiments. The pilotpatterns are represented by relatively small resource blocks 1600-2400,respectively. For illustrative purposes only, it is assumed that theresource blocks 1600-2400 each include six subcarriers and six OFDMsymbols, and are designed for data transmission in an OFDM basedcommunication system transmitting first and second data streams.

Each row of each of the resource blocks 1600-2400 corresponds to asubcarrier of the communication system, and each column of each of theresource blocks 1600-2400 corresponds to an OFDM symbol. The resourceblocks 1600-2400 each include a plurality of OFDM symbols, which furtherinclude a plurality of data symbols each represented by a small blockwith a letter “D,” and a plurality of pilot symbols each represented bya small block with an indexed letter P. For example, the small blockswith indexed letters “P1” and “P2” represent pilot symbols for the firstand second data streams, respectively. In each of the resource blocks1600-2400, each of the OFDM symbols is composed of one of the columns ofdata symbols “D” and any pilot symbols included therein.

For example, in the resource block 1600 shown in FIG. 16, pilot symbolsfor the first data stream (“P1”) have a relatively uniform distributionin the resource block 1600, and are distributed in different OFDMsymbols. Pilot symbols for the second data stream (“P2”) also have arelatively uniform distribution in the resource block 1600, and aredistributed in different OFDM symbols. As a result, power fluctuationbetween OFDM symbols in the resource block 1600 may be reduced, andaccuracy of channel estimation may be improved.

Also for example, in the resource block 1700 shown in FIG. 17, ones ofthe pilot symbols for the first data stream, indicated by dashed circles1702 and 1704, are allocated to boundary subcarriers in the resourceblock 1700, corresponding to the first and last rows of the resourceblock 1700. Ones of the pilot symbols for the second data stream,indicated by dashed circles 1706 and 1708, are also allocated to theboundary subcarriers in the resource block 1700. As a result,extrapolation may be avoided when performing channel estimation based onthe resource block 1700. Therefore, the pilot pattern represented by theresource block 1700 may be used to facilitate channel estimation, andfacilitate pilot allocation for multiple data streams.

Similar to the description above in connection with the resource block1600 (FIG. 16) and the resource block 1700 (FIG. 17), the pilot patternsrepresented by the resource blocks 1800-2400 shown in FIGS. 18-24,respectively, may be used to facilitate channel estimation, andfacilitate pilot allocation for multiple data streams.

In exemplary embodiments, a number of pilot symbols in each of theresource blocks 1600-2400 (FIGS. 16-24) may be reduced, to reducecommunication overhead. FIGS. 25-30 show exemplary pilot patterns eachhaving a reduced number of pilot symbols and configured based on theabove-described rules, according to exemplary embodiments. The pilotpatterns are represented by relatively small resource blocks 2500-3000,respectively. For illustrative purposes only, it is assumed that theresource blocks 2500-3000 each include six subcarriers and six OFDMsymbols, and are designed for data transmission in an OFDM basedcommunication system transmitting first and second data streams.

In exemplary embodiments, a given pilot pattern may be varied togenerate a new pilot pattern, based on a symmetrical mapping of pilotsymbols in a resource block representing the given pilot pattern. FIG.31 shows an exemplary, new pilot pattern generated by varying a givenpilot pattern based on symmetrical mapping, according to an exemplaryembodiment. The given and new pilot patterns are represented by resourceblocks 3110 and 3120, respectively. The resource block 3110 includes aplurality of OFDM symbols, which further include a plurality of datasymbols each represented by a small block with a letter “D” and aplurality of pilot symbols each represented by a small block with aletter P. For example, the small blocks with indexed letters “P1” and“P2” represent pilot symbols for first and second data streams,respectively. In the resource block 3110, each of the OFDM symbols iscomposed of one of the columns of data symbols “D” and any pilot symbolsincluded therein.

In one exemplary embodiment, a symmetrical mapping may be performed onthe pilot symbols in the resource block 3110 with respect to a timereference or a frequency reference. For example, all of the pilotsymbols in the resource block 3110 may be reflected across a timereference 3112 to generate the resource block 3120, as indicated by thedashed arrows. As a result, the new pilot pattern, represented by theresource block 3120, is generated.

In exemplary embodiments, a symmetrical mapping of pilot symbols may beperformed on ones of the pilot symbols in the resource block 3110. Forexample, a symmetrical mapping may be performed on pilot symbols 3120 inthe resource block 3110 with respect to a time reference 3114, togenerate a new pilot pattern (not shown).

In exemplary embodiments, a given pilot pattern may be varied togenerate a new pilot pattern, based on a cyclic shift of pilot symbolsin a resource block representing the given pilot pattern. FIGS. 32A and328 each show an exemplary, new pilot pattern generated by varying agiven pilot pattern based on the cyclic shift, according to an exemplaryembodiment. The given pilot pattern is represented by a resource block3210. For example, the resource block 3210 is the same as the resourceblock 3110 shown in FIG. 31. The generated, new pilot patterns arerepresented by resource blocks 3220 and 3230 in FIGS. 32A and 328,respectively.

In one exemplary embodiment, shown in FIG. 32A, a cyclic shift in timeis performed on the pilot symbols in the resource block 3210 to generatethe resource block 3220. For example, the pilot symbols allocated to afirst time/OFDM symbol in the resource block 3210, indicated by a dashedcircle 3212, are shifted to a second time/OFDM symbol in the resourceblock 3220, indicated by a dashed circle 3222. Also for example, thepilot symbols allocated to a last time/OFDM symbol in the resource block3210, indicated by a dashed circle 3214, are shifted to the firsttime/OFDM symbol in the resource block 3220, indicated by a dashedcircle 3224.

In one exemplary embodiment, shown in FIG. 328, a cyclic shift infrequency is performed on the pilot symbols in the resource block 3210to generate the resource block 3230. For example, the pilot symbolsallocated to a first subcarrier in the resource block 3210, indicated bya dashed circle 3216, are shifted to a second subcarrier in the resourceblock 3230, indicated by a dashed circle 3232. Also for example, thepilot symbols allocated to a last subcarrier in the resource block 3210,indicated by a dashed circle 3218, are shifted to the first subcarrierin the resource block 3230, indicated by a dashed circle 3234.

In exemplary embodiments, either of a cyclic shift in time and a cyclicshift in frequency may be performed for a given pilot pattern togenerate a new pilot pattern. Alternatively, a cyclic shift in time anda cyclic shift in frequency may be jointly performed for a given pilotpattern to generate a new pilot pattern.

In exemplary embodiments, a given pilot pattern may be varied togenerate a new pilot pattern, based on a rotational shift of pilotsymbols in a resource block representing the given pilot pattern. FIG.33 shows an exemplary, new pilot pattern generated by varying a givenpilot pattern based on the rotational shift, according to an exemplaryembodiment. The given and new pilot patterns are represented by resourceblocks 3310 and 3320, respectively. The resource block 3310 includes aplurality of OFDM symbols, which further include a plurality of datasymbols each represented by a small block with a letter “D” and aplurality of pilot symbols each represented by a small block with aletter P. For example, the small blocks with indexed letters “P1” and“P2” represent pilot symbols for first and second data streams,respectively. In the resource block 3310, each of the OFDM symbols iscomposed of one of the columns of data symbols “D” and any pilot symbolsincluded therein.

In one exemplary embodiment, a rotational shift may be performed on thepilot symbols in the resource block 3310 with respect to a center of theresource block 3310, to generate the resource block 3320. For example, arotational shift by one small block along a dashed loop 3312 may beperformed on the pilot symbols in the resource block 3310. As a result,the new pilot pattern, represented by the resource block 3320, isgenerated.

As described above, a new pilot pattern may be generated based on agiven pilot pattern by interchanging positions of pilot symbols in aresource block representing the given pilot pattern. In exemplaryembodiments, this method may also be applied to a relatively smallresource block.

FIG. 34 shows an exemplary, new pilot pattern generated based on a givenpilot pattern by interchanging positions of pilot symbols in a resourceblock representing the given pilot pattern, according to an exemplaryembodiment. The given and new pilot patterns are represented by resourceblocks 3410 and 3420, respectively. For example, the resource block 3410is the same as the resource block 3110 shown in FIG. 31. The resourceblock 3410 includes a plurality of pilot clusters such as pilot clusters3412 and 3414.

In exemplary embodiments, positions of the pilot symbols P1 and P2 ineach of the pilot clusters 3412 and 3414 may be interchanged. Forexample, the pilot cluster 3412 in the resource block 3410 becomes apilot cluster 3422 in the resource block 3420 after the interchanging.Also for example, the pilot cluster 3414 in the resource block 3410becomes a pilot cluster 3424 in the resource block 3420 after theinterchanging. As a result, the new pilot pattern, represented by theresource block 3420, is generated.

In exemplary embodiments, a new pilot pattern may be generated bycombining two or more pilot patterns. The generated pilot pattern may bereferred to as an interlaced pilot pattern. The two or more pilotpatterns each may be a given pilot pattern, such as the pilot patternrepresented by the resource block 3110 (FIG. 31), or a new pilot patterngenerated based on methods consistent with the present invention.Different interlaced pilot patterns may correspond to differentcommunication overheads.

In exemplary embodiments, a new pilot pattern may be generated based ona given pilot pattern, wherein the new pilot pattern and the given pilotpattern may include a different number of OFDM symbols and/or adifferent number of subcarrier frequencies. FIG. 35 shows an exemplary,new pilot pattern generated based on a given pilot pattern, according toan exemplary embodiment. For example, the given and new pilot patternsare represented by resource blocks 3510 and 3520, respectively, and thenew pilot pattern includes a reduced number of OFDM symbols.

In the illustrated embodiment, the resource block 3510 includes, e.g.,six OFDM symbols S1, S2, . . . , S6, which further include a pluralityof data symbols each represented by a small block with a letter “D” anda plurality of pilot symbols each represented by a small block with aletter P. For example, the small blocks with indexed letters “P1” and“P2” represent pilot symbols for first and second data streams,respectively. In the resource block 3510, each of the OFDM symbols iscomposed of one of the columns of data symbols “D” and any pilot symbolsincluded therein.

In exemplary embodiments, ones of the OFDM symbols, e.g., the OFDMsymbols S3 and S4, in the resource block 3510 may be superposed togenerate the resource block 3520 to include a reduced number of OFDMsymbols, such as OFDM symbols S1′, S2′, . . . , S5′. For example, OFDMsymbols including a relatively smaller number of pilot symbols may beselected for the superposition, and extrapolation generally needs to beavoided. Also for example, superposition of data symbols, e.g., datasymbols 3512 and 3514, in the resource block 3510 may result in a datasymbol 3522 in the resource block 3520. Further for example,superposition of a pilot symbol and a data symbol, e.g., a pilot symbol3516 and a data symbol 3518, in the resource block 3510 may result in apilot symbol 3526 in the resource block 3520.

After the superposition, the OFDM symbols 51, S2, S5 and S6 in theresource block 3510 correspond to the OFDM symbols S1′, S2′, S4′ and S5′in the resource block 3520, respectively. As a result, the new pilotpattern with a reduced number of OFDM symbols, represented by theresource block 3520, is generated.

FIG. 36 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment. For example, thegiven and new pilot patterns are represented by resource blocks 3610 and3620, respectively, and the new pilot pattern includes a reduced numberof OFDM symbols. In the illustrated embodiment, the resource block 3610is the same as the resource block 3510 (FIG. 35).

In exemplary embodiments, one or more of the OFDM symbols, e.g., theOFDM symbol S4, in the resource block 3610 may be removed to generatethe resource block 3620 to include a reduced number of OFDM symbols,such as OFDM symbols S1′, S2′, . . . , S5′. For example, an OFDM symbolincluding a relatively smaller number of pilot symbols may be removed,and extrapolation generally needs to be avoided.

After the removal, the OFDM symbols S1, S2, S3, S5 and S6 in theresource block 3610 correspond to the OFDM symbols S1′, S2′, S3′, S4′and S5′ in the resource block 3620, respectively. As a result, the newpilot pattern with a reduced number of OFDM symbols, represented by theresource block 3620, is generated.

FIG. 37 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment. For example, thegiven and new pilot patterns are represented by resource blocks 3710 and3720, respectively, and the new pilot pattern includes an increasednumber of OFDM symbols. In the illustrated embodiment, the resourceblock 3710 is the same as the resource block 3510 (FIG. 35).

In exemplary embodiments, one or more OFDM symbols may be inserted intothe resource block 3710 to generate the resource block 3720 to includean increased number of OFDM symbols, such as OFDM symbols S1′, S2′, . .. , ST. For example, an inserted OFDM symbol may include pilot symbolsto be allocated to subcarriers that have not carried pilot symbols inthe resource block 3710. Also for example, an OFDM symbol includingpilot symbols that may avoid or minimize extrapolation may be inserted.The inserted OFDM symbol may be at a boundary or interior of theresource block 3710.

For example, the OFDM symbol S4′ may be inserted to generate theresource block 3720. After the insertion, the OFDM symbols S1, S2, S3,S4, S5 and S6 in the resource block 3710 correspond to the OFDM symbolsS1′, S2′, S3′, S5′, S6′, and ST in the resource block 3720,respectively. As a result, the new pilot pattern with an increasednumber of OFDM symbols, represented by the resource block 3720, isgenerated.

FIG. 38 shows an exemplary, new pilot pattern generated based on a givenpilot pattern, according to an exemplary embodiment. For example, thegiven and new pilot patterns are represented by resource blocks 3810 and3820, respectively, and the new pilot pattern includes an increasednumber of OFDM symbols. In the illustrated embodiment, the resourceblock 3810 is the same as the resource block 3510 (FIG. 35).

In exemplary embodiments, one or more of the OFDM symbols in theresource block 3810 may be repeated, and be appended to the OFDM symbolsto generate the resource block 3820 to include an increased number ofOFDM symbols, such as OFDM symbols S1′, S2′, . . . , ST. For example,the OFDM symbol S1 in the resource block 3810 may be repeated andappended to the resource block 3810 to generate the resource block 3820.As a result, the new pilot pattern with an increased number of OFDMsymbols, represented by the resource block 3820, is generated.

In exemplary embodiments, a new pilot pattern may be generated bychanging a size of a resource block representing a given pilot patternin the subcarrier or the frequency domain, i.e., changing a number ofsubcarriers or frequencies in the resource block, similar to thedescription above in connection with reducing or increasing a number ofOFDM symbols in a resource block representing a given pilot pattern.Furthermore, a new pilot pattern may be generated by changing both anumber of OFDM symbols and a number of subcarriers in a resource blockrepresenting a given pilot pattern.

In exemplary embodiments, pilot patterns with a variable pilot overheadmay be generated for long delay spread channels. FIGS. 39-42 showexemplary pilot patterns for long delay spread channels, according toexemplary embodiments. The pilot patterns are represented by resourceblocks. For illustrative purposes only, it is assumed that the resourceblocks each include eighteen subcarriers and six OFDM symbols, and aredesigned for data transmission in an OFDM based communication systemtransmitting first and second data streams.

For example, resource blocks 3910 and 3920 shown in FIG. 39 each have apilot overhead of 12.96% approximately. Also for example, resourceblocks 4010, 4020, and 4030 shown in FIG. 40 each have a pilot overheadof 14.81% approximately. Further for example, resource blocks 4110,4120, and 4130 shown in FIG. 41 each have a pilot overhead of 16.67%approximately. As another example, resource blocks 4210 and 4220 shownin FIG. 42 each have a pilot overhead of 18.5% approximately.

In exemplary embodiments, pilot patterns for long delay spread channelsmay be generated based on different methods or rules described above.For example, data symbols may be allocated in a resource block to formas many pairs of data symbols as possible, which may support data-pairbased permutation and the SFBC application. Pilot symbols may also beallocated to form as many pairs of pilot symbols as possible, and thepairs of pilot symbols may be distributed in the resource block as farapart in frequency as possible. In addition, each OFDM symbol maycontain an approximately equal power for each data stream.

FIG. 43 illustrates an apparatus for generating a pilot pattern for datato be transmitted in the above noted OFDM based communication system,according to an exemplary embodiment. As shown FIG. 43, the apparatus430 at least comprises a data modulation module 431, a data symbolallocation module 432, an IFFT module 433, a pilot modulation module 434and a pilot symbol allocation module 435 for allocating pilot symbolsfor a plurality of data streams to form a plurality of pilot clusters inthe pilot pattern, For example, data may be processed through the datamodulation module 431, the data symbol allocation module 432 to the IFFTmodule 433 and pilots are processed through the pilot modulation module434, the pilot symbol allocation module 435 to the IFFT module 433 toallocate pilot symbols for a plurality of data streams to form aplurality of pilot clusters in the pilot pattern

While embodiments have been described based on two or four data streams,the invention is not so limited. It may be practiced with equaleffectiveness with greater or fewer data streams.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. The scope of the invention is intended tocover any variations, uses, or adaptations of the invention followingthe general principles thereof and including such departures from thepresent disclosure as come within known or customary practice in theart. It is intended that the specification and examples be considered asexemplary only, with a true scope and spirit of the invention beingindicated by the following claims.

It will be appreciated that the present invention is not limited to theexact construction that has been described above and illustrated in theaccompanying drawings, and that various modifications and changes can bemade without departing from the scope thereof. It is intended that thescope of the invention only be limited by the appended claims.

What is claimed is:
 1. An apparatus for generating a pilot pattern fordata to be transmitted in an orthogonal frequency-division multiplexing(OFDM) based communication system, comprising: means for allocatingpilot symbols for a plurality of data streams to form a plurality ofpilot clusters in the pilot pattern, wherein each of the pilot clustersincludes ones of the pilot symbols, the ones of the pilot symbols beingfor respectively different ones of the data streams; wherein the pilotpattern is a first pilot pattern represented by a resource block; meansfor moving at least one of the pilot clusters from a first location inthe resource block to a second location in the resource block togenerate a second pilot pattern, the first and second locations beingsymmetrical in time; and means for generating a third pilot patternbased on the first and second pilot patterns.
 2. An apparatus forgenerating a pilot pattern for data to be transmitted in an orthogonalfrequency-division multiplexing (OFDM) based communication system,comprising: means for allocating first and second pilot symbols forfirst and second ones of a plurality of data streams, respectively, to asame subcarrier of the communication system, the first and second pilotsymbols corresponding to a same time, wherein the pilot pattern isrepresented by first and second resource blocks; means for allocatingthird and fourth pilot symbols to first and second boundary times in thefirst resource block, respectively, the third and fourth pilot symbolsbeing for third and fourth ones of the plurality of data streams; andmeans for symmetrically shifting the third and fourth pilot symbols fromthe boundary times to intermediate times in the first resource block. 3.A method for generating a new pilot pattern for data to be transmittedin an orthogonal frequency-division multiplexing (OFDM) basedcommunication system including a transmitter, the method comprising:generating, by the transmitter, the new pilot pattern based on a givenpilot pattern including a plurality of pilot symbols.
 4. The method ofclaim 3, wherein the generating comprises: performing, by thetransmitter, a symmetrical mapping on ones of the plurality of pilotsymbols in the given pilot pattern to generate the new pilot pattern. 5.The method of claim 4, wherein the ones of the plurality of pilotsymbols are allocated to a first subcarrier frequency in the given pilotpattern, the performing comprising: allocating, by the transmitter, theones of the plurality of pilot symbols to a second subcarrier frequencyfor the new pilot pattern, the first and second subcarrier frequenciesbeing symmetrical with respect to a reference frequency.
 6. The methodof claim 4, wherein the ones of the plurality of pilot symbols areallocated to a first time in the given pilot pattern, the performingcomprising: allocating, by the transmitter, the ones of the plurality ofpilot symbols to a second time for the new pilot pattern, the first andsecond times being symmetrical with respect to a reference time.
 7. Themethod of claim 3, wherein the generating comprises: performing, by thetransmitter, a cyclic shift on the plurality of pilot symbols in thegiven pilot pattern to generate the new pilot pattern.
 8. The method ofclaim 7, wherein the performing comprises: performing, by thetransmitter, the cyclic shift in time.
 9. The method of claim 7, whereinthe performing comprises: performing, by the transmitter, the cyclicshift in frequency.
 10. The method of claim 3, wherein the generatingcomprises: performing, by the transmitter, a rotational shift on ones ofthe plurality of pilot symbols in the given pilot pattern to generatethe new pilot pattern.
 11. The method of claim 3, wherein the givenpilot pattern is represented by a resource block including a pluralityof OFDM symbols, the generating comprising: superposing, by thetransmitter, first and second ones of the plurality of OFDM symbols inthe resource block to generate the new pilot pattern.